With The Forbidden Zone, director Katie Mitchell and writer Duncan Macmillan have created an upsetting, compelling story of war without ever setting foot on the front line. Created to commemorate the First World War, the piece reminds us of the many barbarous ways soldiers were killed in their droves. But it also looks at how wartime moves people to sacrifice their morality: the perception of what is inhumane quickly shifts as the drive to win takes over.

One of the most arresting things about the piece is its true story. You probably won't have come across scientist Clara Immerwahr, but her tale, and that of three decades of her family, is remarkable. Immerwahr was a brilliant scientist at the turn of the century - unusual for a woman - and in 1901 she married fellow scientist Fritz Harber who would later be awarded the Nobel Prize.

Harber's work in the field of chemical warfare, (he was also largely responsible for the success of modern fertiliser), unsettled his wife. While Harber continued with his research during wartime, seeing it as necessary for the war effort, Immerwahr became increasingly against it. Eventually in 1915, after her husband enabled the first devastating use of chlorine gas on the front line in Germany, she shot herself at their home. There is debate about exactly why, but evidence points towards her inability to reconcile her husband's work with her sense of right and wrong.

The piece focuses both on this tragedy and on the way Immerwahr and Harber's actions echo through the generations. Their granddaughter, also a scientist but this time in 1949, is continuously appalled by the way her grandfather's invention mutilates and murders. Her end is not dissimilar to her grandmother's.

Mitchell uses onstage cameras to weave together the different strands of The Forbidden Zone, which features poetic text written by Virginia Woolf, Mary Borden, Simone de Beauvoir and others. Essentially we watch the action play out on a huge screen at the top of the stage, while the scenes are shot live from the set below it. Cameramen scurry around quickly and quietly as they zoom in on the actors.

The set is astonishingly intricate and detailed. Much of the play happens on an American train from the '40s which feels real on both the big screen and on the stage itself. Right from the unforgiving lighting, to the dirty windows, it has been lovingly and meticulously constructed. The train moves - it opens, shuts and breaks in two to reveal scenes at the back of the stage which are also filmed. From the audience, you can't see them close up: only catch glimpses. The action is played out in full, larger than life, on the screen overhead.

To begin with, this distancing from the action is awkward: why stage a live play simultaneously live onscreen? But as The Forbidden Zone progresses, watching both mediums together brings much to the atmosphere and intensity of the piece. It is a unique experience - not quite theatre and not quite film.

The Forbidden Zone is a remarkable achievement of timing and cues: a balancing act performed by not just actors but by cameramen too. And it's intriguing just for that. But the piece is also a quietly overwhelming look at the heavy destruction of conflict, and the ease with which humans shrug off their humanity.

The Forbidden Zone runs at the Barbican until May 29.